* {
  margin: 0;
  padding: 0;
}
html,
body {
  height: 100%;
  overflow: hidden;
}
.wrap {
  height: 100%;
  overflow: auto;
}
.wrap .content {
  height: 200%;
}
.wrap .content .returntop {
  position: absolute;
  right: 50px;
  bottom: 50px;
  width: 50px;
  height: 50px;
  background-color: #acf;
}
